The impact of health insurance on access to care and health outcomes has been studied extensively. Much less is known about the spillover effects of one person's health insurance coverage on the health care utilization and health outcomes of other patients. This project explores the consequences of health insurance coverage not just for those who are covered, but for the quantity and quality of care provided throughout the health care system. Understanding the wider consequences of changes in the scope of health insurance coverage for particular patient groups is a key component in evaluating the broader effects of government health insurance programs such as Medicare and Medicaid: if many of the benefits of coverage expansions accrue to patients not directly affected by the coverage, then analyses of both private and public policies that do not take these spillovers into account may come to incorrect conclusions about the optimal scope, source and structure of health insurance coverage. First, this project will identify the existence and magnitude of the spillover effects of health insurance coverage. We will do this by examining the effects of increases in Medicaid generosity through the Disproportionate Share Hospital (DSH) program on hospital spending for personnel and capital equipment, both for Medicaid patients and non-Medicaid patients. We will then trace out the effects of those spending changes on patient health outcomes. Second, this project will explore the channels through which these health and spending spillovers occur, such as joint production of health across different populations, imperfect differentiation of insurance status by providers, provider preferences, and direct health spillovers. We will distinguish among these spillover mechanisms by examining the different populations, diseases, and treatments in which spillovers are concentrated. We will explore the implications of these different mechanisms for health policy, such as the relative efficiency of subsidies for health insurance purchase, direct provision of care, subsidies for technology adoption, and Medicare and Medicaid eligibility and reimbursement structures. [unreadable] [unreadable] [unreadable]